In the fabrication of an optical lens, particularly a spectacle lens, in order to improve the light-shielding properties, anti-glaring properties, photochromic properties, anti-scratch properties, and the like, a coating film is formed on the surface of the spectacle lens using a material that matches the object of the spectacle lens. Formation of the coating film is described in “Spectacles”, May 22, 1986, pp. 81 to 83, published by Kabushiki Kaisha Medical Aoi Shuppan. An apparatus that forms a coating film automatically is disclosed in Japanese Patent Laid-Open Nos. 2000-334369, 2004-290857, and the like.
The lens coating apparatus described in Japanese Patent Laid-Open No. 2000-334369 automatically performs a series of steps from the step of applying a coating solution to a lens surface to the step of curing the coating solution by ultraviolet irradiation. When curing the coating solution, air in a curing station is purged with nitrogen gas.
The coating apparatus described in Japanese Patent Laid-Open No. 2004-290857 comprises a photopolymerization chamber where photopolymerization takes place and a photopolymerization preliminary chamber serving as a front chamber of the photopolymerization chamber. Air in the two chambers is purged with an inert gas. When polymerizing a photocuring coating agent, a lens coated with the coating agent is stored in the polymerization preliminary chamber in advance, and air in the preliminary chamber is purged with nitrogen gas. Then, the lens is moved to the photopolymerization chamber and irradiated with ultraviolet radiation to polymerize the coating agent. The polymerization preliminary chamber is provided to shorten the time required for purging the nitrogen gas in the photopolymerization chamber to obtain a uniform film thickness and prevent color shading and a decrease in lens optical characteristics.
As the material of the coating film to form on the spectacle lens, a UV-curing resin added with a photopolymerization initiator is usually used. As the photopolymerization initiator, a mixture of two types of UV polymerization initiators that contribute to internal curing and surface curing is used. As the internal curing UV polymerization initiator, generally, bisacylphosphine oxide (BAPO) or bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide is used. As the surface curing UV polymerization initiator, 1-hydroxy-cyclohexyl-phenyl-ketone described in, e.g., Japanese Patent Laid-Open No. 2000-334369 is used. BAPO is a polymerization initiator that can increase the photosensitivity on the long wavelength side to promote curing of the interior deep in the film, and is very effective particularly as the material of a pigment or ink coating which has a large thickness and low optical transmittance.